Cage proteins form macromolecules. Macromolecules have molecular weights that are tens to hundreds of times larger than those of low-molecular weight monomers due to a precise self-assembly property of monomers. Viral capsid proteins, ferritins, heat shock proteins, and DNA-binding proteins from strayed cells (Dps proteins) are classified as cage proteins. While cage proteins are hollow inside, each monomer constituting a cage protein has a very regular and precise interaction with adjacent monomers. Since the inside of the cage protein is isolated from the outside of the cage protein (due to the nature of the container-like property of the cage protein) the cage protein is frequently used as a drug delivery system in the medical field.
Researches are actively researching viral vectors and non-viral vectors in the cage protein-applied material transport field. Currently, adenovirus is often studied as a viral vectors and ferritins and heat shock proteins are studied as non-viral vectors. However, the conventional viral vectors have been reported to cause in vivo safety problems due to the genes of the viruses.
Ferritin is a kind of intracellular protein, while functioning to store and release iron. Ferritin is generally in the form of a hollow spherical cage in vivo. The cage is composed of 24 subunits. The subunits are divided into heavy chains and light chains depending on their structures.
Although human-derived ferritin protein does not have the safety problems involved with viral vectors, human-derived ferritin protein mave have diminished specific binding affinity where a targeting moiety binds to a certain region. In some cases, the human-derived ferritin protein does not form a cage. Therefore, there is an urgent need to develop fusion polypeptides that can be effectively delivered to a target by enhancing specific affinity of a targeting moiety that may effectively form a cage (i.e., have no problems in the formation of a cage).
The above information disclosed in this Background section is only for enhancement of understanding of the background of the inventive concept, and, therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.